In a full color printer, the quality of the printer output relies on the printer parameters remaining within their respective calibration limits. This typically means that the optical densities of each color must be maintained within prescribed values. For many printers, this is accomplished by generating printed samples of each color at predetermined parameter settings and then manually taking optical density measurements of the samples with an external densitometer or other equivalent density sensing instrument. Then if the measured densities vary from the expected densities, the operator based upon experience manually makes corrections to the printer parameters to bring the optical densities of each color into the prescribed limits.
This is a tedious and long process and the results are error prone. First, the tolerance limits prescribed by the printer manufacturer are often too large, resulting in unacceptable color shifts. Second, the process for obtaining the optical densities are not automated and are prone to two types of operator error. The first type of operator error is that the operator can easily confuse or forget the density readings manually taken. The second type of operator error is that the operator may lack the skill or experience to take the appropriate corrective action. In addition, even a skilled operator may not make optimal corrections because of the intricate nature of the various parameter changes on toner density at the various levels.